Manufacture of plasters



Patented May 6, 1941 h UNITED STATES PATENT OFFICE 2,240,529 MANUFACTURE OF PLASTERS George Crawford Tyce, Norton-on-Tees, and Victor Lei'ebure, London, England, assignors to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Application March 11, 1936, Serial No. 68,350. In Great Britain March 13, 1935 11 Claims. (Cl. 260-29) This invention relates to the manufactur of ton or linen; ground glass, fine silver sand, plasters, particularly plasters having incorposuitably graded alabaster or marble chippings, or rated therein a resin. aggregates consisting of set plaster as described It is an object of this invention to provide a in U. S. specification No. 60,543. The presence plaster, or similar cementitious material, with of such aggregates is of advantage in overcoma glossy appearance, and one that can easily ing a possible tendency of the surfaces of the be moulded into any desired shape, or on to any products to crack or "craze. Pigments may also required surface, and has the advantage that it be incorporated in'the slurry to give any desired sets rapidly to an extremely hard condition. decorative effect.

According to one form of our invention, we We have found that a plaster substantially free prepare a slurry of a calcium sulphate plaster, from impurities such as iron, silica and alumina or example, plaster of Paris, and'a cold-hardengives the most satisfactory results. Such a plasing urea-formaldehyde for thiourea-formaldeter sets hard and retains its whiteness when slurhyde resin syrup, such as may be obtained for ried with the maximum amount of resin syrup. example by condensing urea or thiourea and Examples of plasters of this nature, which have formaldehyde in aqueous medium and removing been found to give excellent results are those a portion of the water, water being added if necknown as fine boiled hemihydrate plasters. essary to obtain the desired consistency. The The ratio of resin syrup to plaster is not critior unstabilised type. Preferably a resin syrup of of resin syrup to 3 parts of plaster. The minithe unstabilised type is employed, 1. e. one withmum ratio has been 1 part of resin syrup to 10 out the addition of NHiCl or other stabilising parts of plaster, plus the amount of water neces'. material. It may, if desired, be accelerated with sary to form a slurry. The higher ratio of resin acid or acid salts to obtain a short setting time. confers extra hardness and extra gloss on the set Th setting time of the mix is shorter than the product. setting time of the resin syrup and longer than The maximum permissible ratio of resin syrup the setting time of plaster and water alone. to plaster varies with different types of plaster. While in the plastic state the slurry may be With fine boiled hemihydrate plaster the ratio cast or moulded or even trowelled or rolled on appears to be unlimited, but with accelerated anto surfaces. The more dilute slurries may be hydrite plaster the maximum ratio is 100 parts applied to surfaces by brushing 0r spraying. of plaster to 8 parts of resin syrup. Accelerated When the set has occurred a glossy face is proanhydrite plaster consists essentially of finely duced which on drying out, either in the air or ground mineral anhydrite mixed with small proin a drying chamber, becomes extremely hard. portions of certain metal sulphates acting as ac- It is then amenable to working by chiselling, turning or sawing. The hardened products re- A suitable procedure for veneering building semble alabaster in appearance and are of uniblocks is as follows. In this process an enhydrite form colour, unless deliberately modified by adbuilding block consisting of plaster of cellular mixture of aggregates or pigments. Th hardstructure such as that described in U. S. speciening of the resin and th setting of the plaster 40 fication No. 2,015,481 receives a veneer of the do not proceed independently, but each is iniluplaster-resin product, either plain or incorporatenced by the other. The water required for the ins pi ments designed to give the app n e f hydration and setting of the plasteriswithdrawn m r l W ra nin 1' the like. The resin from the resin syrup, while the accelerators presyr p. either accelerated or unaccelerated and cut may affect both resin and plaster. Owing to either plasti ed or npl i i d, is mixedintithe continued presence of water in the mass the mately with th fin o l d hemihydrate plaster. net change of volume on setting is comparatively A suitable mixture is 100 parts by weight or plassmall, so that the surfaces do not tend to crack. ter, 40 parts of a 45% urea-formaldehyde resin Glycerol, sugars, alginates or other water-solsyrup and 2% of a 25% solution of HCl. Design uble softening agents may be added to the resin is introduced into the mix by incorporating pigyrup orslurry, in order to obtain products 01' ments. The mix is placed on a glass, Celluloid, varying degrees of elasticity. ebonite, oiled steel or the like, plate and tamped. Fillers or aggregates of various kinds may be Finally the block is forced into the plastic and incorporated in the slurry, for example fibrous left until the "set has taken place. The block material such as disintegrated paper, wool, cotis then lifted away from the glass face and alhard and glossy.

The finished product is extremely and has the appearance of good lowed to dry.

' tine effects.

Example A plaster block measuring 2 ft. x 1 it. was veneered to a thickness of as follows:

1.5 kg. of a fine boiled hemi-hydrate plaster such as that known in the trade under the name Cafierata was thoroughly mixed with g. disintegrated paper and then gauged with 680 cc. urea-formaldehyde resin syrup, 150 cc. of water and 7 cc. of hydrochloric-acid. The result-. ing plastic mass was laid on a polished glass plate and tamped to remove air bubbles. The plaster block was to ensure good adhesion. After about 45 minutes the veneered block was stripped from the glass plate and dried at 40 C. The stripped surface was very highly polished;

Our plaster-resin slurries are also suitable for application by brushing or spraying, water being used as a diluent able glossy surfaces can readily be obtained on walls, ceilings and other surfaces without the necessity of using paints requiring relatively expensive organic solvents or thinners. Moreover, difficulties due to the use of oil paints on plaster, cement or the like, resulting in non-uniform contact and subsequent cracking and blistering, are avoided by the use of our slurries. The presence of water and the absence of organic solvents, coupled with the presence of a water-setting i plaster in the slurry make it possible to effect very rapid decorative treatments which are extremely durable. By allowing to set in contact with a superposed polished surface, which is' subsequently stripped off, permanently glossy surfaces are obtained.

Various modifications may be made in the materials and procedure hereinbefore described, and all such modifications are intended to come within the scope of the appended claims in so far as they achieve to a useful degree the new results and advantages hereinbefore disclosed.

We claim:

l. A process for the manufacture of a, plaster suitable forcasting, moulding, trowelling, rolling, brushing or spraying, and capable of setting to a hard glossy mass amenable to working by chiselling, turning, sawing or the like, which comprises preparing an aqueous slurry of an accelerated anhydrite plaster and a cold-hardening aqueous resin syrup containing an acid accelerator which does not react with said accelerated anhydrite plaster, said resin. syrup being selected from the classconsisting of urea-formaldehyde and thioureaformaldehyde resin syrups,

where necessary. Thus durthe applied slurry the like then laid firmly into this mass 'by chiselling,

comprises preparing an aqueous slurry of an acerator which does not anhydrite plaster, said resin syrup being selectlonging to inass comprising the the proportion of resin syrup to plaster not exceeding parts of plaster to 8 parts of syrup.

2. A process as set forth in claim 1, in which water is added to the slurry to obtain the desired.

consistency.

3. A process as set forth in claim 1, in which the resin syrup is of the unstabilised type.

4. In a process for the manufacture of a plaster suitable for casting, moulding, trowelling, rolling, brushing or spraying, and capable of setting to a hard glossy mass amenable to working by chiselling, turning, sawing or the like, which comprises preparing an aqueous slurry of an accelerated anhydrite plaster and a coldhardening aqueous resin syrup containing an acid accelerator which does not react with said accelerated anhydrite plaster, said resin syrup being selected from the class consisting of ureaformaldehyde and thiourea-formaldehyde resin syrups, the proportion of resin syrup to plaster not exceeding 100 parts of plaster to 8 parts of syrup, the step of incorporating a water-soluble softening agent.

5. A process as set forth in claim 4, in which the water-soluble softening agent is selected from the class consisting of glycerol, sugars and alginates.

6. In a process ter suitable for casting, moulding, trowellin rolling, brushing, or spraying, and capable of setting to a hard glossy mass amenable to working turning, sawing or the like, which celerated anhydrite plaster and a cold-hardening aqueous resin syrup containing an acid accelreact with said accelerated ed from the class consisting of urea-formaldehyde and thioureaformaldehyde resin syrups,

the proportion of resin syrup to plaster not exceeding 100 parts of plaster to 8 parts of syrup, the step of incorporating a comminuted filler selected from the class consisting of fibrous materials and natural and artificial mineral substances.

l. A process as set forth in claim 6, in which the filler is selected from the class consisting of disintegrated paper, wool, cotton and linen.

8. A process as set forth in the filler is an artificially prepared aggregate consisting essentially of set plaster. '9. A hard elastic mass consisting essentially of'a homogeneous mixture of a set accelerated anhydrite plaster and a cold-hardened resin bethe class consisting of urea-formaldehydeand thioureaformaldehyde resins, said cold-hardened reaction product of not more than 100 parts of plaster to 8 parts of resin syrup.

l0. A-mass as set forth in claim 9, comprising a comminuted filler.

11. A mass as set forth in a comminuted fibrous filler.

GEORGE CRAWFORD 'I'YCE. VICTOR LEFEBURE.

claim 9, comprising for the manufacture of a plasclaim 6, in which n 

